rced by necessity to labour, their excitability
becomes exhausted in a proper and natural manner, and they retire to
rest early in the evening. Their sleep is generally sound, and early
in the morning they find themselves recruited, and in a state fit to
resume their daily labour. The blooming complexion, strength, and
activity, of these hardy children of labour, who recruit their
wearied limbs on pallets of straw, form a striking contrast with the
pallid and sickly visage, and debilitated constitution of the
luxurious and wealthy, who convert night into day, and court repose
in vain on beds of down. Nature undoubtedly intended that we should
be awake, and follow our occupations, whether of pleasure or
business, during the cheering light of day, and take repose when the
sun withdraws his rays. All other animals, and even vegetables, obey
the command of nature: man alone is refractory; but nature's laws are
never violated with impunity. Dr. Mackenzie very properly observes,
that those who sleep long in the morning, and sit up all the night,
injure the constitution without gaining time: and those who do this
merely in compliance with fashion, ought not to repine at a
fashionable state of bad health.

From what has been said, it is evident that, in order to enjoy sound
sleep, our chambers should be free from noise, dark, and moderately
cold; because the stimulant effects of noise, light, and heat,
prevent the accumulation of excitability: and as we shall afterwards
see that this accumulation depends on free respiration, and the
introduction of oxygen by that means into the system, our bed rooms
ought to be large and airy, and, in general, the beds should not be
surrounded by curtains. We may from this likewise see the reason why
it is so desirable to sleep in the country, even though we are
obliged to spend the day in town.

These observations on sleep have however led me a little from the
direct road; but I thought they could not be better introduced than
here. I shall now return to the subject of our more immediate
inquiry.

By induction we have discovered two of the principal laws by which
living bodies are governed: the first is, that when the ordinary
powers which support life have been suspended, or their action has
been lessened for a time, the excitability, or vital principle,
accumulates, or becomes more fit to receive their actions; and
secondly, when these powers have acted violently, or for a
considerable